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| Titel |
Long and short time variations of the Na/K ratio in the exosphere of Mercury. |
| VerfasserIn |
Alessandro Mura, Helmut Lammer, Peter Wurz, Stefano Orsini, Anna Milillo, Valeria Mangano, Herbert I. M. Lichtenegger, Manuel Scherf, Maxim Khodachenko, Martin Pfleger |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250099523
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| Publikation (Nr.) |
 EGU/EGU2014-15314.pdf |
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| Zusammenfassung |
| Here we present the results of our model for the short-time and yearly
variations of the Sodium and Potassium exosphere of Mercury. Such
surface-bounded exosphere is produced by release processes occurring
at the planetary surface, such as ion sputtering, thermal- or photon-stimulated
desorption. The amount of surface Sodium or Potassium that is
available for release, however, is limited. Those release processes
deplete the surface in Na and K, which is continuously refilled by
diffusion from the interior of regolith grains or by chemical
sputtering. Ejected particles may either escape the gravity field,
assisted by the radiation pressure acceleration, or be photoionized,
or fall back onto the surface. Falling particles will stick to the
surface.
A Montecarlo model, simulating all these processes, is used to obtain
the exosphere densities and the Na/K ratio, taking into account
the planet's orbit and rotation speed. The influence of variations of the
solar wind precipitation (i.e., CMEs) is also included. We compare
this model with either ground- and space-based observations of the
exosphere and tail to evaluate the effectiveness of each source
process. We find that including a source process which effectiveness
is proportional to the precipitation of solar wind protons, is
necessary to explain most of the available observations in both
qualitative and quantitative way. We find that, to reproduce dawn-dusk
asymmetries, we need to include the rotation of Mercury's surface in
the model. After finding the correct model parameter by calibrating
the model with observation, we simulate the short-term and yearly
variations of Na/K. |
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